Possible diseased oak tree
Though we can't see the leaves too distinctly, this is probably oak anthracnose, a fungal disease. It is common in many species of shade trees when we have a prolonged period of wet, overcast days--as we did recently. (Actually, the sycamores got hit much harder than the oaks.) Mature native trees can weather this disease without last effects because they have co-evolved with the disease and are able to adapt to it.
Here is information what to do about anthracnose from our website:http://extension.umd.edu/hgic/shade-tree-anthracnose-trees
This should not occur every year, but only when weather conditions are just right.